Delta-v (Δv) is the total change in velocity a rocket must produce to accomplish a mission. It is the single most important parameter in space mission design — once you know the Δv, the rocket equation tells you how much propellant is needed, and the propellant requirement determines the vehicle size and cost.
Δv is additive: a mission that requires several maneuvers has a total Δv equal to the sum of each maneuver’s Δv. This makes it a budget — you start with the Δv your propulsion system can deliver (determined by specific impulse and mass ratio), and you spend it on each mission phase.
The delta-v map
Key delta-v values for Earth-based missions:
| Maneuver | Δv (km/s) | Notes |
|---|---|---|
| Surface to LEO (200 km) | 9.3–9.5 | Includes ~1.5 km/s gravity/drag losses |
| LEO to GTO | 2.5 | Transfer orbit to geostationary altitude |
| GTO to GEO | 1.5 | Circularization at GEO |
| LEO to Moon transfer | 3.1 | Trans-lunar injection |
| Moon orbit to surface | 1.7 | Lunar descent |
| LEO to Mars transfer | 3.6 | Hohmann transfer, favorable opposition |
| Mars orbit to surface | 1.0 | With aerobraking: ~0.05 km/s |
| LEO to Earth escape | 3.2 | C3 = 0 |
The dominant cost is always the first maneuver — getting off Earth’s surface. The 9.4 km/s to LEO is more than the Δv from LEO to Mars. This is why “once you’re in orbit, you’re halfway to anywhere” (Robert Heinlein) — though not in terms of travel time.
Gravity losses and drag losses
The ideal Δv for a circular orbit at 200 km is just the orbital velocity: 7.8 km/s. Real rockets need 9.3–9.5 km/s because:
- Gravity loss (~1,000–1,500 m/s): while climbing vertically, gravity accelerates the rocket downward. Every second spent fighting gravity rather than building horizontal velocity is wasted Δv.
- Drag loss (~100–400 m/s): atmospheric drag slows the rocket during the dense-atmosphere phase of ascent.
- Steering loss (~50–100 m/s): the gravity turn trajectory is not perfectly efficient.
Delta-v as design driver
The Δv budget drives every aspect of launch vehicle design:
- Propellant choice — higher I_sp means less propellant for a given Δv
- Staging — more stages allow higher total Δv from practical mass ratios
- Trajectory — gravity turns and aerobraking reduce propulsive Δv requirements
- Payload mass — every kilogram of payload reduces the achievable Δv
Related terms
- Rocket Equation — the equation linking Δv to mass ratio and exhaust velocity
- Specific Impulse — determines how much propellant a given Δv requires
- Orbital Mechanics — the physics that determines how much Δv each maneuver requires
- Gravity Turn — the ascent trajectory that minimizes gravity losses